Following this story last night, I found it difficult to sift through the massive amounts of bullshit (with so many commenters immediately jumping to "it's nothing!" or "lock him up!" and doing everything to obfuscate the facts). So in the spirit of trying to have clean discussion in the newly re-opened section here, I'm just going to post my understanding of what the story actually is, in case it is helpful to anyone else.
1. Research on Trump was performed by a private company, originally hired on behalf of Republican primary opponents then employed by Democrats after the primary was over. This company employed the "former MI6 official with ties to Russia" to conduct the research. This research is ostensibly the source of the 35 pages of memos that was published by Buzzfeed (so worth noting I think that is this document is not purported to be a government intelligence document).
2. The memos from this research ended up being known to US intelligence and numerous politicians and journalists last year (possibly via the British government) before the election. However, probably since the claims were so spectacular and were unverified, few news outlets published anything from them. An exception was Mother Jones which published a story on 31 October saying that a veteran spy from a Western nation had provided information on Trump's connection with Russia to the FBI. Since they were the only organisation (as far as I know) that published anything on it at the time and they couldn't provide further evidence, it got buried by more concrete stories and became just another rumour.
3. After the election, as the discussion regarding Russian interference in the election increased, the memos from the oppo research were circulating around politicians and journalists. John McCain, apparently bothered enough by their contents to think they needed to be investigated further, personally presented them to the director of the FBI (as I understand it the FBI probably already had them and were carrying out their own investigation).
4. Shortly after this, an intelligence briefing was presented to President Obama and President-Elect Trump on the subject of the investigation into the Russian interference in the election. The existence and information contained in the memos was part of the briefing (though not the only content).
5. CNN, aware of the existence of this intelligence briefing and that the memos (which they had had for some time but felt unable to report on until further investigation could confirm the claims) were being discussed, reported , factually, that Obama and Trump were briefed on the information contained in the memos, and described the gist of some of that information.
6. Buzzfeed then published the memos in their entirety - noting that they were unverified and may contain inaccuracy, but claiming that they were "letting the people decide".
So the important points worth mentioning that from what I have seen might get lost in the chaos or amongst other disinformation are that the "memos" published by Buzzfeed aren't claimed to be government documents, but oppo research conducted by a veteran British MI6 official (who has been described as reliable and has the credentials to at least carry out information like this by numerous journalists and government officials), and that the story broke by CNN was not simply the content of the memos, but rather that the president and president-elect had been briefed by US intelligence leaders about information which *included* those memos. Also the story reported by CNN is distinct from the dump of the memos by Buzzfeed.
There is also another narrative which I saw emerge, one which involves a site which is banned here (a rule I agree with in principle as I consider it to be basically the mainstream scumhole of the internet, but that makes discussing this element of the story a little difficult

). Without going into specifics that would break a rule, here is my understanding of this narrative and the facts that support it.
1. At some point in October, an anonymous poster on this unmentionable site claimed to have convinced a journalist (I believe a right-wing, "Never Trump" type) that there was going to be another leak of something related to Trump, possibly another sex tape. The idea was that journalists would be fooled and believe someting then be embarassed, "for the lulz" (it's important to note that stuff like this is a common feature of this site - as is anonymous posters posting complete bullshit).
2. After Mother Jones posted the story at the end of October, an anonymous poster posted on the unmentionable site that his attempt to fool the media had been successful, that they had took his information and "added a Russian spy angle to it" and ran with it. Many kekz were had.
3. Once the CNN / Buzzfeed story broke, the connection with the Mother Jones story and the unmentionable site was made... and there was a massive deluge of comments around the internet claiming that the mainstream media had been trolled, and that the memos were actualy produced by a troll who talked about it on the unmentionable site (these comments also conflated this document with actual fake documents and stories recently produced, which Buzzfeed didn't actually report). *This next part is my complete personal impression, but witnessing the volume and nature of comments last night that attempted to push the narrative that the entire thing was the media / intelligence services being fooled by trolls, I was very much reminded of the type of trolling usually associated with the unmentionable site trolls that they use to attempt to fool people.
You can draw your own conclusions, but personally I don't think the "unmentionable site narrative" holds up at all, and the evidence for it is extremely slim. (For example, note that the post that supposedly proves that trolls were responsible for providing the information actually says that it was the media that added the "Russian spy stuff"... which makes it kind of hard to claim that the troll provided the memo full of Russian spy stuff

). Plus, if the intent was genuinely to fool the media, why work so hard to make sure everyone is aware that the story is "false" as soon as you have fooled them? In my opinion if the unmentionable site trolls manage to "fool" anyone, it is by convincing people that the story is based on deliberately made up evidence intended to fool the media. (Also I would say that convincing people of this falsehood works better for their beloved Trump, rather than convincing the media to run extremely embarassing stories about Trump).
That's my take on the actual timeline and facts of what the story actually
is, in terms of who is actually saying what - plus a little editorialising by me, but I hope the parts that are meant to be my personal impression rather than fact are clear enough. It took me a little while to get straight what was actually being reported and by who, so hopefully it is of some help to someone

. If there are any corrections please let me know as I think it'd be helpful if we were all at least discussing the same thing.